1. Field of the Invention
The present invention relates generally to multifiber ferrules and methods for their manufacture, and more specifically, to improved methods for manufacturing multifiber ferrule assemblies having improved bumper height tolerances and region of interest surface finishes.
2. Technical Background
Multiple optical fibers, either presented in individual or ribbonized form, are commonly terminated using multifiber connectors. In order to interconnect these fibers with a minimum amount of attenuation, corresponding multifiber connectors may be mated such that opposing optical fibers are biased into contact with one another. To achieve optimal transmission without utilizing refractive index matching gel, the multifiber connectors are precisely core aligned and are in physical contact. Fine connector alignment is typically provided by a pair of guide pins that seat within bores to provide a male ferrule. The guide pins protrude from the connective end of the male ferrule and are received within corresponding guide pin bores defined by a female ferrule upon mating. In addition to ferrule alignment, the geometry of the ferrule and, in particular, the polish geometry of the end face of the ferrule, is extremely important to insure proper fiber-to-fiber contact and coplanarity between fibers. In this regard, at least the portion of the end face of each ferrule that is proximate to the optical fibers, referred to herein as the “region of interest,” is preferably polished and/or processed to define a plane extending perpendicular to the longitudinal axis defined by the guide pin bores and, therefore, perpendicular to the optical fiber bores. In addition, the planar surface defined by the portion of the end face of each ferrule proximate to the fiber openings is precisely positioned relative to the ends of the optical fibers. For example, with proper polish/process geometry, the optical fibers will extend by a predetermined distance beyond the end face of the ferrule so that fiber-to-fiber contact between opposing optical fibers is established. If, however, the polish/process geometry is not precisely defined, fiber-to-fiber contact may be prevented or otherwise obstructed by contact between those portions of the end faces of the opposing ferrules that extend beyond the ends of the optical fibers.
Conventional ferrules available from Corning Cable Systems of Hickory, N.C., include not only a ferrule body defining guide pin and fiber bores, but also include polishing bumpers that function as a polishing reference surface for polishing the optical fibers to a proper height from the end face and achieving the appropriate coplanarity between fibers. With regard to ferrules having a generally rectangular end face, a polishing bumper is typically located about each side of the region of interest of the end face. While the fiber bores typically open through the region of interest, the guide pin bores typically open through the bumpers. Once the optical fibers have been polished to their proper predetermined height, the bumpers are typically ground away or removed to a depth recessed from the region of interest so that they do not physically contact bumpers of a mating connector. Thus, after fiber polishing, the bumpers are ground to a height less than the protrusion of the optical fibers themselves.
Referring to prior art FIGS. 1 and 2, a conventional multifiber ferrule 10 and a conventional multifiber ferrule molding insert 10′ are shown. The multifiber ferrule 10 includes a generally rectangular end face forming portion 12 and bumper forming portions (not numbered). Guide pin bore forming pins are held within guide pin openings 16. Fiber bore forming pins are held within fiber pin openings 18. Turning to FIG. 2, multifiber ferrule insert 10′ used for molding conventional multifiber ferrule 10 includes bumper forming portions that are formed and/or processed by an electrical discharge machining (EDM) process (indicated by the shaded region marked as 24), and the region of interest 20 is conventionally formed and/or processed by a surface grind process (indicated by the shaded region marked as 26). These processing techniques are apparent to manufacturers when viewing processing marks left on the connective end of the molding insert under magnification.
Referring to FIGS. 3-5, a conventional ferrule molding insert whose end face was EDM and surface ground processed was analyzed for surface finish and flatness. Referring specifically to FIG. 3, a graphical plot representation of the resulting roughness of the end face surface of an EDM processed insert yielded an average roughness (Ra) of 0.4877 μm. Referring specifically to FIGS. 4-5, graphical plot representations of the end face surface finish and flatness resulting from the sample ferrule insert having its region of interest processed by surface grinding is shown, respectively. As shown, the surface finish of the region of interest yields an Ra of 0.266 μm (FIG. 4) and a flatness across the fiber area of 1.9 μm (FIG. 5).
Current tolerances for polishing bumper heights are about 15+/−5 microns. However, to improve manufacturing yields, it would be desirable to control the tolerance on the bumper height more precisely. Specifically, it would be desirable to establish acceptable tolerances on the order of 15+/−3 microns. Still further, it would be desirable to establish tolerances of 15+/−2 microns. Further, with respect to the region of interest, current tolerances are 94 nm Ra. Accordingly, it would be desirable to develop an improved ferrule insert surface processing method to improve the surface finish of the region of interest of a molded ferrule. A ferrule molding insert having an improved surface finish and flatness will translate into a ferrule having an improved surface finish and flatness. Thus, what is desired are improved multifiber ferrule molding insert processing methods.